1. Field of the Invention
This invention relates to new polymeric colorants which find especial utility as yellow food colors.
2. The Prior Art
FD&C Yellow #5, a monoazo dye of the formula ##STR2## commonly known as tartrazine, has a "lemon yellow" hue which has placed it among the three most widely used colors in foods, drugs and cosmetics. It finds use alone in gelatin desserts, jellies, beverages and the like and as a component of orange through green blends for use in both edibles and nonedibles.
The past decade has seen a sustained attack on the general class of monoazo food colors. A number of these materials, most notably Reds No. 2 and No. 4, have been found to be unsafe and banned from food use by governmental action. There is continuing questioning of the safety of the monoazo colorants which is causing a search to be made for properly hued, safe replacements. In the case of tartrazine, certain natural carotinoid colors can function as replacements. However, the carotinoids are relatively very expensive. The present invention seeks to provide a nonazo color replacement for the yellow colorant tartrazine. This invention concerns a limited class of polymeric nitrosulfanilic acid colorants. The advantage of polymeric colorants in food coloring applications is disclosed in general terms in U.S. Pat. No. 3,920,855, issued Nov. 18, 1975 to Dawson et al., in copending United States Patent application, Ser. No. 520,530, filed Nov. 4, 1975, by Gless et al. now U.S. Pat. No. 4,018,826, and in Japanese Patent Applications of Tanabe, such as 41-14433, 41-14434, and 41-13382. These references show that when colorants are employed in polymeric form having a molecular size exceeding a certain limit--usually a molecular size of greater than 1,000 or 2,000 daltons--and if the color compounds do not break down in use, and thus maintain this size, the polymeric colorants are not absorbed through the walls of the gastrointestinal tract. This means that when such colorants are ingested, they pass essentially directly through the gastrointestinal tract. They are not taken through the tract walls into the body or its systemic circulation. Thus, risk of systemic toxicity is reduced or eliminated. The present invention is an extension of these prior art disclosures and involves a family of polymeric colorants having particularly attractive color properties.